Numerical study on the effects of spark strategies on knocking combustion in a downsized gasoline rotary engine

The application of dual-spark plug in rotary engines (REs) could be regarded as an effective way to improve combustion performance but there is lack of researches about influence of spark strategies on RE knocking. For this reason, the effects of varying dual-spark plug locations and asynchronous ignition phases on local auto-ignition and knocking characteristics of a downsized gasoline RE were studied numerically in this paper. Results showed that asynchronous ignition strategies formed by delaying the trailing-spark ignition timing significantly reduced the knocking intensity (KI) and delayed timing of auto-ignition onset. The appropriate asynchronous ignition phase could induce multiple auto-ignition hot-spots, and the KI caused by multiple hot-spots formed in sequence was higher than that caused by a single hot spot. The arrangement of the dual-spark plug determined the space for flame development, and it was favorable in reducing the KI for the trailing-spark plug to stand an offset from the minor axis of the engine. It should be noted that the KI of the RE was reduced by 87% when the offset distance between the trailing-spark plug location and the minor axis was double that between the leading-spark plug location and the minor axis.